<div class="refentry" lang="en" xml:lang="en"><a id="gluTessVertex"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>gluTessVertex — specify a vertex on a polygon</p></div><div class="refsynopsisdiv"><h2>C Specification</h2><div class="funcsynopsis"><table><tr><td><code class="funcdef">void <b class="fsfunc">gluTessVertex</b>(</code></td><td>GLUtesselator*  </td><td><var class="pdparam">tess</var>, </td></tr><tr><td> </td><td>GLdouble *  </td><td><var class="pdparam">location</var>, </td></tr><tr><td> </td><td>GLvoid*  </td><td><var class="pdparam">data</var><code>)</code>;</td></tr></table></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="parameters"></a><h2>Parameters</h2><div class="variablelist"><dl><dt><span class="term"><em class="parameter"><code>tess</code></em></span></dt><dd><p>
                    Specifies the tessellation object (created with <a class="citerefentry" href="gluNewTess"><span class="citerefentry"><span class="refentrytitle">gluNewTess</span></span></a>).
                </p></dd><dt><span class="term"><em class="parameter"><code>location</code></em></span></dt><dd><p>
                    Specifies the location of the vertex.
                </p></dd><dt><span class="term"><em class="parameter"><code>data</code></em></span></dt><dd><p>
                    Specifies an opaque pointer passed back to the program with the vertex callback
                    (as specified by <a class="citerefentry" href="gluTessCallback"><span class="citerefentry"><span class="refentrytitle">gluTessCallback</span></span></a>).
                </p></dd></dl></div></div><div class="refsect1" lang="en" xml:lang="en"><a id="description"></a><h2>Description</h2><p>
            <code class="function">gluTessVertex</code> describes a vertex on a polygon that the program defines. Successive
            <code class="function">gluTessVertex</code> calls describe a closed contour. For example,
            to describe a quadrilateral, <code class="function">gluTessVertex</code> should be called four times.
            <code class="function">gluTessVertex</code> can only be called between <a class="citerefentry" href="gluTessBeginContour"><span class="citerefentry"><span class="refentrytitle">gluTessBeginContour</span></span></a> and
            <a class="citerefentry" href="gluTessEndContour"><span class="citerefentry"><span class="refentrytitle">gluTessEndContour</span></span></a>.
        </p><p>
            <em class="parameter"><code>data</code></em> normally points to a structure containing the vertex
            location, as well as other per-vertex attributes such as color and normal.
            This pointer is passed back to the user through the <code class="constant">GLU_TESS_VERTEX</code>
            or <code class="constant">GLU_TESS_VERTEX_DATA</code> callback after tessellation
            (see the <a class="citerefentry" href="gluTessCallback"><span class="citerefentry"><span class="refentrytitle">gluTessCallback</span></span></a> reference page).
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="example"></a><h2>Example</h2><p>
            A quadrilateral with a triangular hole in it can be described as follows:
            </p><pre class="programlisting">
gluTessBeginPolygon(tobj, NULL);
   gluTessBeginContour(tobj);
      gluTessVertex(tobj, v1, v1);
      gluTessVertex(tobj, v2, v2);
      gluTessVertex(tobj, v3, v3);
      gluTessVertex(tobj, v4, v4);
   gluTessEndContour(tobj);
   gluTessBeginContour(tobj);
      gluTessVertex(tobj, v5, v5);
      gluTessVertex(tobj, v6, v6);
      gluTessVertex(tobj, v7, v7);
   gluTessEndContour(tobj);
gluTessEndPolygon(tobj);
            </pre><p>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><a id="notes"></a><h2>Notes</h2><p>
            It is a common error to use a local variable for <em class="parameter"><code>location</code></em> or <em class="parameter"><code>data</code></em> and store
            values into it as part of a loop.
            For example:
            </p><pre class="programlisting">
for (i = 0; i &lt; NVERTICES; ++i) {
   GLdouble data[3];
   data[0] = vertex[i][0];
   data[1] = vertex[i][1];
   data[2] = vertex[i][2];
   gluTessVertex(tobj, data, data);
}
            </pre><p>
        </p><p>
            This doesn't work.
            Because the pointers specified by <em class="parameter"><code>location</code></em> and <em class="parameter"><code>data</code></em> might not be
            dereferenced until <a class="citerefentry" href="gluTessEndPolygon"><span class="citerefentry"><span class="refentrytitle">gluTessEndPolygon</span></span></a> is executed,
            all the vertex coordinates but the very last set could be overwritten
            before tessellation begins.
        </p><p>
            Two common symptoms of this problem are when the data consists of a single
            point (when a local variable is used for <em class="parameter"><code>data</code></em>) and a
            <code class="constant">GLU_TESS_NEED_COMBINE_CALLBACK</code> error (when a local variable is
            used for <em class="parameter"><code>location</code></em>).
        </p></div>
        {$pipelinestall}{$examples}
        <div class="refsect1" lang="en" xml:lang="en"><a id="seealso"></a><h2>See Also</h2><p>
            <a class="citerefentry" href="gluNewTess"><span class="citerefentry"><span class="refentrytitle">gluNewTess</span></span></a>,
            <a class="citerefentry" href="gluTessBeginContour"><span class="citerefentry"><span class="refentrytitle">gluTessBeginContour</span></span></a>,
            <a class="citerefentry" href="gluTessBeginPolygon"><span class="citerefentry"><span class="refentrytitle">gluTessBeginPolygon</span></span></a>,
            <a class="citerefentry" href="gluTessCallback"><span class="citerefentry"><span class="refentrytitle">gluTessCallback</span></span></a>,
            <a class="citerefentry" href="gluTessEndPolygon"><span class="citerefentry"><span class="refentrytitle">gluTessEndPolygon</span></span></a>,
            <a class="citerefentry" href="gluTessNormal"><span class="citerefentry"><span class="refentrytitle">gluTessNormal</span></span></a>,
            <a class="citerefentry" href="gluTessProperty"><span class="citerefentry"><span class="refentrytitle">gluTessProperty</span></span></a>
        </p></div><div class="refsect1" lang="en" xml:lang="en"><div id="Copyright"><h2>Copyright</h2><p>
            Copyright © 1991-2006
            Silicon Graphics, Inc. This document is licensed under the SGI
            Free Software B License. For details, see
            <a class="ulink" href="http://oss.sgi.com/projects/FreeB/" target="_top">http://oss.sgi.com/projects/FreeB/</a>.
        </p></div></div></div>
